Tape drives are being improved in order to accommodate increased tape cartridge capacities and data rates. Increases in tape cartridge capacities are achievable by increasing the linear data density and the number of data tracks written across the width of tape. Increases in data rates are achievable by increasing the number of parallel data channels and the tape velocity.
Increases in tape cartridge capacities and data rates are limited by the available read back signal-to-noise ratio (SNR). This limitation results because the physical read width in linear flexible media recording systems is proportionally smaller than the physical write width in order to provide the servo system with sufficient margin to correctly position the read sensor within the previously written track during read-back operation. Thus, as the track pitch is reduced, the physical read width is proportionally reduced resulting in a decrease in the read signal and thereby a loss in SNR.
Certain read sensors use the anisotropic magneto-resistance (AMR) effect. The AMR effect causes the intrinsic resistance of an AMR sensor to be a function of the relative angle between the direction of the electric current flow in the sensor and its magnetic moment. The AMR effect has a maximum amplitude of roughly 2.5% of the intrinsic resistance of the sensor. The available signal can be increased somewhat by reducing the thickness of the sensor in order to increase its resistance or by increasing the electric current flow in the sensor. However, the absolute amplitude of the read-back signal is limited by both the maximum current density achievable without damaging the sensor film stack and the temperature rise of the sensor.
These issues can be mitigated by using read-back sensors which use the giant magneto-resistive (GMR) effect. The GMR effect results in sensor resistance changes of more than 10%. However, GMR sensors are formed from extremely thin films (<5 nm) of which several of these films (e.g., Cu, NiMn, PtMn) may have significant corrosion issues. As flexible media systems read with the sensor essentially in contact with the surface of the tape this inevitably exposes the sensor to corrosive agents, in addition to abrasion and smearing of the film stack at the sensor edge exposed to the tape. An additional drawback of GMR based devices is the adverse effects of electro-static discharge (ESD). During an ESD event, a charge build-up is rapidly dissipated through the sensor and other components of the GMR based device. The damage results in catastrophic changes such as device melting or evaporation, and/or the magnetic integrity of the device.
The above disadvantages result in significant processing and reliability issues which currently limit the use of MR (including GMR and AMR) read-back sensors in a flexible media environment such as magnetic tape.